Many areas in the world have implemented varying degrees of Low Emissions Zones (LEZ) including Zero Emissions Zones (ZEZ). As an example, in some locations, older busses and trucks that do not meet certain emissions standards are not allowed. In still other locations, vehicles with internal combustion engines are not allowed, and hybrid vehicles are allowed only if operating in an electric-only mode with the internal combustion engine off.
There may be circumstances when a vehicle is entering or passing through such an area (e.g., LEZ or ZEZ) where the vehicle batteries are not at the optimum level to get to the destination and back, or even to pass through the area. For example, there may not be sufficient margin around the estimated energy needs. Even if an engine driven battery charging device is available on-board the vehicle, it may be difficult to charge the battery as rapidly as required when operating the vehicle in such an area.
The inventors herein have recognized that the motor of an electrically assisted boosted engine system may be used to address the above issue. In particular, boosted engine systems may be provided with electric machines to provide electrical assistance, such as an electric motor/generator coupled to a turbocharger. The motor can drive the supercharger compressor or the turbocharger shaft to improve transient boost pressure delivery during a tip-in event. During conditions when rapid battery charging is required, such as just before entering a ZEZ, a turbocharger may be run at a higher power than necessary while the electric motor is operated in a recuperating mode to charge the system battery, or other energy storage device, at a faster rate than would otherwise be possible. In addition to expediting battery charging, an energy recuperation potential of the motor/generator is increased. Further still, the operation of the electric motor of the boosted engine system can be coordinated with the operation of an electric motor coupled to the driveline of the hybrid electric vehicle (such as a starter-motor) to charge the battery while meeting the driver torque demand.
In one example, rapid battery charging may be enabled by a method for a hybrid vehicle having a boosted engine, comprising: responsive to anticipated vehicle operation in a low emission zone, charging a system battery via at least one of a first electric motor coupled to a turbocharger shaft and a second electric motor coupled to a vehicle driveline, the charging of the system battery completed before the vehicle enters the zero emission zone. The same approach may also be applied during conditions when engine-driven battery charging is not available, such as when an alternator is degraded.
As one example, while a hybrid electric vehicle is propelled using engine torque, a vehicle controller may predict that vehicle travel through a low emissions zone (LEZ) is upcoming based on input from a navigational system. The controller may then calculate an amount and rate of charge transfer required to the system battery to enable the vehicle to be propelled using motor torque when in the LEZ. For example, based on a current state of charge (SOC) of the battery, and further based on a distance or duration of travel (from a current location) before entering the LEZ, as well as a distance or duration to be traveled while in the LEZ, the controller may calculate a target SOC for the battery. An amount and rate of charge transfer may then be determined in accordance. To enable the expedited charging of the battery, motor torque from one or both of a first electric motor that is coupled to a turbocharger of the vehicle system, and a second electric motor coupled to a driveline of the vehicle system, may be applied. For example, based on current engine speed-load conditions, which vary with operator torque demand, the controller may vary the ratio of negative motor torque applied to charge the battery, while using concurrent waste-gate and intake throttle adjustments to maintain wheel torque based on the operator torque demand. For example, during conditions when boosted engine operation with electric assistance from the first electric motor is not required, the boost request may be increased in excess of the operator torque demand, thereby closing the waste-gate more than required, and the excess turbocharger torque may be used to charge the battery via the first electric motor. As another example, during conditions when there is a drop in torque demand, boost pressure may be decreased by absorbing torque from the turbocharger shaft and using it to charge the battery via the first motor, while also absorbing wheel torque and using it to charge the battery via the second motor. A ratio of torque absorbed at the first motor relative to the second motor may be adjusted based on overall system needs (such as by absorbing more torque via the first motor when the drop in torque demand is larger) as well as motor conditions (such as by absorbing more torque via the first motor when a temperature of the second motor is higher than its optimal value).
In this way, by working the turbocharger harder than required for the requested vehicle tractive effort, a system battery can be charged faster than would otherwise be possible. The technical effect of varying the ratio of motor torque drawn from an electric assist motor and a hybrid vehicle driveline electric motor to charge the battery is that a target SOC can be achieved while continuing to provide driver demanded torque. By charging the battery before entering a low emissions zone, emissions compliant vehicle operation in the low emissions zone can be enabled. By also charging the battery using motor torque from the electric assist motor during conditions when an alternator is degraded, a minimum battery charge can be maintained at all times, improving the performance of a hybrid electric vehicle.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.